Packaged, pre-cut fresh apples are appealing to consumers and food service operators because they are convenient, ready-to-use, and produce little or no waste for the consumers or food service operators. Cut apple pieces may be used as a snack, as an ingredient for mixed fruit salads, as a fruit topping for a dessert, for fruit juice preparation, or in many other applications. To be successful in the marketplace, the packaged, pre-cut apple pieces preferably retain acceptable quality attributes during storage periods of up to four weeks at refrigerated temperatures.
Cutting fresh apples bruises the parenchyma tissue of the apples and breaks cell walls, which results in decompartmentization of the cellular contents. Such tissue damage can lead to undesirable quality changes in the apples, such as:                1. increase in respiration rate;        2. acceleration in ripening and senescence;        3. reduction in textural crispness and firmness;        4. enhanced enzymatic browning; and        5. increased microbial contamination and growth.        
With an increase in respiration rate, the acidity of the apple tissue is reduced due to respiratory catabolism of the organic acids and an increased amount of carbon dioxide is produced. Large amounts of carbon dioxide can lead to excessive carbonation of the apple tissue. If the apples are packaged, excess carbon dioxide production can also cause ballooning of sealed flexible plastic packages. It is therefore desirable to reduce the respiration rate of packaged cut apples.
The firmness of cut apple pieces decreases steadily during refrigerated storage. This reduction in firmness can be attributed to the breakdown of intercellular pectic substances during ripening, which is triggered by ethylene. The biosynthesis of ethylene is accelerated when apple tissue is damaged during the cutting process. The sensory attributes of crispness are related to the firmness of apple tissue, to the strength of intercellular bridging, and to the level of cellular turgor, the protoplasmic fluid pressure on the cell walls. Reducing ripening reactions, particularly reducing ethylene synthesis, can assist in maintaining the crisp texture of cut apple pieces.
When fresh apples are cut into pieces and exposed to the air, the tissue surfaces become brown within a few hours. The rate of cut apple browning depends on the age of the apple, the cultivar and the level of tissue damage on the cut surfaces. Browning is brought about by the enzymatic conversion of naturally-occurring phenolic compounds to quinones, which subsequently react non-enzymatically to form brown-coloured polymers called melanins. Enzymatic browning of cut apple pieces can be attributed to the action of polyphenol oxidase on the phenolic compound substrates in the presence of oxygen. The formation of brown-colored melanins on the surfaces of cut apple pieces can be inhibited by inactivating the polyphenol oxidase, maintaining the phenolic compounds in a reduced state, or preventing oxygen from coming into contact with the cut apple surfaces.
Sulfites in solution have been used to prevent enzymatic browning by inactivating polyphenol oxidase and reducing quinones. A citric acid solution with added ascorbic acid has also been employed as a dip solution for cut apple pieces to inhibit browning. Citric acid lowers the pH of the apple below the optimum level for polyphenol oxidase activity (pH 6.2). Ascorbic acid in dip solutions can interrupt the chemical reaction of browning by reducing quinone compounds to the dihydroxy phenolic forms.
Functional additives can be added to cut apple pieces to inhibit specific quality deteriorative changes during prolonged refrigerated storage. However, some additives can lead to undesirable textural changes and off-flavour development. For example, citric acid in a dip solution can cause an increase in sourness of apple pieces. Calcium salts have been used as firming agents, but at high concentrations they can impart a bitter taste in the apple pieces and can contribute to a leathery texture in place of the normally crisp texture associated with apples. Methodologies for reducing or eliminating these undesirable textural changes and off-flavour development brought about by functional additives would be beneficial.
U.S. Pat. No. 5,939,117, Chen et al., Aug. 17, 1999 discloses methods of preserving fresh fruit with fresh fruit preservatives which extend the shelf life of fresh fruit particularly fresh cut fruit, are provided. The fresh fruit preservative preserves the texture, flavor, appearance, crispness, and color of the fresh fruit, particularly the exposed skin of the fresh fruit. The method includes the following steps: providing a solution of fruit preservative comprising: water, calcium ions; and ascorbate ions, wherein the ascorbate ions and calcium ions are present in a ion ratio of preferably from about 1.5:1 to about 2.5:1 at a near neutral pH of 6.0 to 6.3; and, applying said fruit preservative to the fruit. The fruit is then stored at a temperature which will not freeze the fruit; temperatures of −6° C. have been found not to freeze the apples. Preferably the fruit is stored at temperatures of between about −7° C. to room temperature, about 20° C., more preferably about −2° to about 7° C., most preferably from about 2° C. to about 5° C. The invention also relates to fresh fruits preserved with the fresh fruit preservatives.